This invention relates to a mechanism for limiting the load on a central point in a network architecture. In particular, the illustrated embodiment of the invention relates to a mechanism for limiting the load on a Service Control Point in an Intelligent Networks architecture.
An Intelligent Networks architecture includes a Service Control Point (SCP), which typically has a large number of Service Switching Points (SSP) connected to it. Each SSP is a switching system that can intercept telephone calls, and query the SCP. The SCP contains service specific logic and data, that allows it to return instructions to the SSP on how to deal with the intercepted call.
Clearly, if the SCP receives an excessive number of simultaneous queries from different SSPs, congestion may arise in the network""s signalling links, the processing capability of the SCP may be overloaded, and unacceptable delays in processing the calls may result.
In an existing Intelligent Network specification, ETS 300 374-1, at pages 136-139, call gapping is provided as the only means to reduce signalling traffic sent towards SCPs.
When a SCP detects a high load condition, it sends instructions back to some or all SSPs to begin call gapping, meaning that those SSPs reduce the rate at which they are allowed to send queries to the SCP. However, this mechanism is rather inefficient, because of the delays which exist between the detection of the high load condition by the SCP and the time at which call gapping is initiated by the SSP. The result is that an unexpected peak in the number of SCP queries can still cause the SCP to be overloaded.
In accordance with other existing Intelligent Networks, the SSP has a dynamic mechanism for monitoring the load condition of the SCP, and preventing overload. This is achieved by defining a ceiling for the number of SCP queries awaiting a response, and rejecting call attempts which would take the number of pending queries above that ceiling. Such systems are disclosed in:
1. xe2x80x9cOn load control of an SCP in the Intelligent Networkxe2x80x9d, NYBERG et al, proceedings of the Australian Telecommunication Networks and Applications conference, vol. 2, Jan. 1st, 1994, pages 751-756.
2. xe2x80x9cA study of methods for protecting an SCP from overloadxe2x80x9d, KIHL et al, IEE conference on Telecommunications, Mar. 26th, 1995, pages 125-129.
3. xe2x80x9cCongestion control for Intelligent Networksxe2x80x9d, PHAM et al, International Zurich seminar on Digital Communications Intelligent Networks and their applications, Mar. 16th, 1992, pages 375-389.
4. xe2x80x9cPerformance and overload considerations when introducing IN into an existing networkxe2x80x9d, TSOLAS et al, International Zurich seminar on Digital Communications Intelligent Networks and their applications, Jan. 1st, 1992, pages 407-414.
These have the advantage that the SSP can automatically react to a change in the load condition of the SCP, without requiring any message to be sent from the SCP, allowing faster reaction to an unexpected burst of call attempts.
However, these systems suffer from the disadvantage that the ceiling (or threshold) is only reduced after the system has entered the overload condition. The present invention overcomes this disadvantage by taking corrective action before the overload condition is entered, as will be described below.